GAITHERSBURG, Md. - The National Institute of Standards and Technology (NIST) has announced that a researcher has come up with a method designed to improve the energy efficiency of commercial water chillers. The NIST method, if confirmed through experiments with full-scale chiller systems, could save as much as 1 percent of the 320 billion kWh of electricity used annually by chillers or an equivalent 5.5 million barrels of oil per year, according to Mark Kedzierski, the NIST mechanical engineer who developed the technique.

This advance builds on past NIST research designed to optimize mixtures of chiller refrigerants with lubricants. The researchers discovered that some lubricants, when injected in small amounts, can significantly enhance evaporator heat transfer, increasing the efficiency of chillers. When they studied the process more closely, they found the most efficient heat transfer occurred when the added oil's surface tension, viscosity, composition, and chemical characteristics complemented those of the chiller's base lubricant.

In a recent paper describing the method, Kedzierski describes how the right additive forms a very thin covering on an evaporator surface, which produces enhanced bubbling during boiling. The improved conversion of the refrigerant molecules into vapor molecules increases the chiller's cooling capacity similar to a heat pump.